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From: Peter Maydell <peter.maydell@linaro.org>
Date: Tue, 21 Jul 2015 18:14:40 +0100
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Subject: Re: [Qemu-devel] [RFC 7/7] fw_cfg DMA for x86
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To: =?UTF-8?Q?Marc_Mar=C3=AD?= <markmb@redhat.com>
Cc: Stefan Hajnoczi <stefanha@gmail.com>, Paolo Bonzini <pbonzini@redhat.com>, Kevin O'Connor <kevin@koconnor.net>, QEMU Developers <qemu-devel@nongnu.org>, Gerd Hoffmann <kraxel@redhat.com>

On 21 July 2015 at 17:03, Marc Mar=C3=AD <markmb@redhat.com> wrote:
> Enable fw_cfg for x86 machines. Create new machine to avoid
> incompatibilites.

> @@ -1391,7 +1399,14 @@ FWCfgState *pc_memory_init(MachineState *machine,
>                                          option_rom_mr,
>                                          1);
>
> -    fw_cfg =3D bochs_bios_init();
> +    if (guest_info->fw_cfg_dma) {
> +        as =3D g_malloc(sizeof(*as));
> +        address_space_init(as, ram_below_4g, "pc.as");
> +        fw_cfg =3D bochs_bios_init(as, BIOS_CFG_DMA_ADDR);
> +    } else {
> +        fw_cfg =3D bochs_bios_init(NULL, 0);
> +    }
> +

As with ARM: what's the rationale for choosing this particular
AddressSpace as the target for fw_cfg DMA? (I'm not saying it's
wrong, necessarily -- I was just surprised we didn't just use
the system address space.)

thanks
-- PMM